COS 284-6 - Mapping Spatial and Temporal Dynamics of Katabatic and Foehn Wind Events across the western U.S.

Abstract: The intersection of warm, dry winds and wildfires has resulted in some of the most dramatic impacts on ecosystems and communities alike. These Katabatic and Foehn winds occur at broad and local scales across the western U.S. and include commonly known Santa Anas or Chinook winds, as well as more local winds like the Chetco winds of SW Oregon. While the Santa Anas have been extensively studied, other wind events remain less well studied. In this study, we examined the locality, seasonality, frequency, and duration of these wind events to support decisions in wildfire management and building resilience in the western U.S. to a rapidly changing fire environment. We used GridMET data from 1979-2021 data to identify events using thresholds in relative humidity, wind speed, and wind direction. We explore two categories: 1) major wind events with wind speeds at or exceeding 4 m/s and at or below 36% relative humidity; and 2) extreme events occurred at or exceeding wind speeds of 8 m/s with a relative humidity of 26% or below. Our results showed western wind events were more numerous than the east winds, with extreme events having a large decrease in the number of occurrences. This may be due to the prevailing winds regularly occurring from the west across this western US. Maps were created depicting wind strength and direction. Colorado showed the greatest number of wind events. The Cascades tended to produce wind events with lower wind speeds and higher relative humidity than the Rocky Mountains. Major and extreme wind events all experience a strong seasonality for both east and west wind events. Major east wind events showed a peak occurrence in the early summer or fall except, for southern California which showed peak occurrences in fall and winter. For example, Oregon's largest frequency of occurrence occurred in August with major events at 8.5% and extreme events at 1.8%. Our wind events map aligns with known large fires that have been affected by Katabatic and Foehn wind events. Even with low odds, these wind events during a fire can have significant consequences. Understanding the locality, seasonality, and frequency of these wind events can help improve strategies for managing fire in accordance with social and ecological resilience and enhance decisions in policy and management from communities to natural landscapes.